StructurizeCFG: Fix verification failure with some loops.

If the beginning of the loop was also the entry block
of the function, branches were inserted to the entry block
which isn't allowed. If this occurs, create a new dummy
function entry block that branches to the start of the loop.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@195493 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/Scalar/StructurizeCFG.cpp b/lib/Transforms/Scalar/StructurizeCFG.cpp
index 0124dfdbeb109505441d0ed1b2d9e0e22a248c63..5045ff8fdfda068146e95e7540751828befaeb0c 100644 (file)
--- a/lib/Transforms/Scalar/StructurizeCFG.cpp
+++ b/lib/Transforms/Scalar/StructurizeCFG.cpp
@@ -779,6 +779,20 @@ void StructurizeCFG::handleLoops(bool ExitUseAllowed,
     handleLoops(false, LoopEnd);
   }
 
+  // If the start of the loop is the entry block, we can't branch to it so
+  // insert a new dummy entry block.
+  Function *LoopFunc = LoopStart->getParent();
+  if (LoopStart == &LoopFunc->getEntryBlock()) {
+    LoopStart->setName("entry.orig");
+
+    BasicBlock *NewEntry =
+      BasicBlock::Create(LoopStart->getContext(),
+                         "entry",
+                         LoopFunc,
+                         LoopStart);
+    BranchInst::Create(LoopStart, NewEntry);
+  }
+
   // Create an extra loop end node
   LoopEnd = needPrefix(false);
   BasicBlock *Next = needPostfix(LoopEnd, ExitUseAllowed);

diff --git a/test/Transforms/StructurizeCFG/no-branch-to-entry.ll b/test/Transforms/StructurizeCFG/no-branch-to-entry.ll
new file mode 100644 (file)
index 0000000..2e22c87
--- /dev/null
+++ b/test/Transforms/StructurizeCFG/no-branch-to-entry.ll
@@ -0,0 +1,31 @@
+; RUN: opt -S -o - -structurizecfg < %s | FileCheck %s
+
+; CHECK-LABEL: @no_branch_to_entry_undef(
+; CHECK: entry:
+; CHECK-NEXT: br label %entry.orig
+define void @no_branch_to_entry_undef(i32 addrspace(1)* %out) {
+entry:
+  br i1 undef, label %for.end, label %for.body
+
+for.body:                                         ; preds = %entry, %for.body
+  store i32 999, i32 addrspace(1)* %out, align 4
+  br label %for.body
+
+for.end:                                          ; preds = %Flow
+  ret void
+}
+
+; CHECK-LABEL: @no_branch_to_entry_true(
+; CHECK: entry:
+; CHECK-NEXT: br label %entry.orig
+define void @no_branch_to_entry_true(i32 addrspace(1)* %out) {
+entry:
+  br i1 true, label %for.end, label %for.body
+
+for.body:                                         ; preds = %entry, %for.body
+  store i32 999, i32 addrspace(1)* %out, align 4
+  br label %for.body
+
+for.end:                                          ; preds = %Flow
+  ret void
+}